The primary aim of the proposed work is to study the transport mechanism of levodopa and its derivatives across the brain tissues and renal tubules, and to determine the correlation between these two transport systems and the factors influencing the concentration of these compounds at their site of action and in the plasma. Our studies in the last four years have shown that there is a high degree of structural specificity in renal tubular transport of aromatic amino acids, such as tryptophan and phenylalanine derivatives, and a bidirectional transport system for such compounds. In those studies both the microperfusion technique and clearance techniques were used. It is intended in the proposed work to expand our studies on levodopa transport and to apply our microperfusion skill and facilities to cerebroventricular perfusion. The major objectives are to determine 1. the characteristics of efflux of levodopa and related compounds from the central nervous system using clearance from cerebral ventricles as a model system; 2. the mechanism of renal excretion of levodopa and related compounds 3. the effects of structurally related compounds and metabolic inhibitors on the CNS and renal transport of levodopa.